The invention disclosed herein relates generally to wall mounted thermostats of the type for controlling both heating and cooling apparatus and, more particularly to automatic changeover type thermostats.
In the past, automatic changeover thermostats typically have had two separate temperature responsive elements or bimetals, two separate control point adjustment levers and two separate temperature scales. The heating bimetal and an associated heating switch controlled the heating apparatus and a cooling bimetal and an associated cooling switch controlled the cooling apparatus. In addition one of the bimetals activated a changeover switch which enabled either the heating switch or the cooling switch depending on the temperature in the space.
The heating and cooling control point adjustment levers on these thermostats are typically mechanically linked to allow their adjustment to within 2.degree. F. to 6.degree. F. of one another. The 2.degree. F. to 6.degree. F. separation represents a safety margin to reduce the risk of the thermostat causing both heating and cooling apparatus to operate simultaneously or in response to each other. This margin allows for some error in the calibration of the separate bimetals and for the variable heating anticipation current which results in some I.sup.2 R heating within the thermostat.
Further, the separate bimetal elements, separate set point levers, and separate temperature scales associated with automatic changeover thermostats results in a high cost to the consumer.
Thus a need exists for a simpler and lower cost automatic changeover thermostat.